Ranger 1994 6 American motor cylinders

In December 2010, a Ford Ranger XLT '94 3.0 6 cylinders bought, they made greater tuning but accelerates alone, without accelerating reaches up to 45 km/hr. The mechanics tell me that it is the "yak valve", as this sensor is called and I want to ask a specialized mechanic if this is true. Thank you. Chetumal Q. Roo Mexico